Dipole-Dipole vs Hydrogen Intermolecular Bonds (1 Viewer)

[Pedro123]

Apologies for questions, probably been answered before, just having a bit of a pre-HSC panic.
1. How come the intermolecular bonds formed with a carbonyl group on a molecule (i.e. carboxylic acid, or the non-carbonyl oxygen in the ester group) is defined as forming a dipole-dipole bond, but the bonds formed with the oxygen on the hydroxyl group are classified as hydrogen bonds, when both the carbonyl and the hydroxyl oxygen form them with a hydrogen? (This also applies for the amine group).

2. What is the order of bond strengths/boiling points for organic molecules or similar molar mass? I am under the impression it is:
- Alkanes, Alkenes, Alkynes
- Ketone
- Aldehyde
- Ester
- Alcohol
- Amine
- Carboxylic Acid
- Amide
But some assorted research has come up different? (Where amide and amine are higher than carboxylic acid and alcohol despite the lower strength H bonds due to the increased number of sites for H-Bonds to form)

Thanks

 

[username_2]

Apologies for questions, probably been answered before, just having a bit of a pre-HSC panic.
1. How come the intermolecular bonds formed with a carbonyl group on a molecule (i.e. carboxylic acid, or the non-carbonyl oxygen in the ester group) is defined as forming a dipole-dipole bond, but the bonds formed with the oxygen on the hydroxyl group are classified as hydrogen bonds, when both the carbonyl and the hydroxyl oxygen form them with a hydrogen? (This also applies for the amine group).

2. What is the order of bond strengths/boiling points for organic molecules or similar molar mass? I am under the impression it is:
- Alkanes, Alkenes, Alkynes
- Ketone
- Aldehyde
- Ester
- Alcohol
- Amine
- Carboxylic Acid
- Amide
But some assorted research has come up different? (Where amide and amine are higher than carboxylic acid and alcohol despite the lower strength H bonds due to the increased number of sites for H-Bonds to form)

Thanks

Well... about the first one what you have said is correct - they are hydrogen bonds, all of them - and is also the key reason why stuff like nylon (amine group) and acrylic (CH3COOH) have the properties they do - they are strong partly because of this factor. And also boiling points which you have mentioned in the second part. IN terms of bond strength, the hsc is generally not concerned with the amide/amine boiling points (generally) but as far as I can tell the order tou have written makes sense because the bond strength is strong with a greater difference in electronegativity (hence why amide is higher than carboxylic acid) but amines are not because they have only one polar bond whereas carboxylic acid has two. SO yeah hope that helps

 

[tito981]

Apologies for questions, probably been answered before, just having a bit of a pre-HSC panic.
1. How come the intermolecular bonds formed with a carbonyl group on a molecule (i.e. carboxylic acid, or the non-carbonyl oxygen in the ester group) is defined as forming a dipole-dipole bond, but the bonds formed with the oxygen on the hydroxyl group are classified as hydrogen bonds, when both the carbonyl and the hydroxyl oxygen form them with a hydrogen? (This also applies for the amine group).

2. What is the order of bond strengths/boiling points for organic molecules or similar molar mass? I am under the impression it is:
- Alkanes, Alkenes, Alkynes
- Ketone
- Aldehyde
- Ester
- Alcohol
- Amine
- Carboxylic Acid
- Amide
But some assorted research has come up different? (Where amide and amine are higher than carboxylic acid and alcohol despite the lower strength H bonds due to the increased number of sites for H-Bonds to form)

Thanks

1. for hydrogen bonding, the hydrogen has to be connected to its own oxygen, then it is able to form hydrogen intermolecular bond with an oxygen
from another molecule. carbonyl groups are attached directly to the carbon spine and has no hydrogen attached to it directly. Hence, it can only form dipoles with other molecules. Amines satisfy the hydrogen bond criteria as it has an intermediate nitrogen bond.

2. just swap alcohol and amine and your list is correct. This is because -OH is a more electro-negative group than the amine group, hence it forms stronger hydrogen bonding. For the last part, im not sure why they have put carobxyl and alcohol higher up, could possibly be an error or something im not aware of.

 

[someth1ng]

What you've described sounds like a hydrogen bond to me...an H-bond is essentially a special type of dipole-dipole bond.

For a hydrogen bond, you need:

1. A hydrogen bond donor: the component/molecule which supplies the hydrogen atom. The donor must have a sufficiently large charge separation, usually by being bonded to nitrogen, oxygen, or fluorine.
2. A hydrogen bond acceptor: the component/molecule with a lone pair (e.g. ketones, alcohols, amines, ethers). The accepting atom must have a high electron density (and a negative formal charge), typically nitrogen, oxygen, or fluorine.

Extended Discussion (non-syllabus):

• Hydrogen bond donors are distinct from typical dipole-dipole bonds because is significant orbital overlap so an H-bond is partially covalent (this is also what makes H-bonds directional).
• It comes down to matching orbital sizes/energies when you have N/O/F and an H-N/O/F, which enables this interaction.
• When people say H-bonding requires N/O/F because they are highly electronegative, they often ignore that Cl is more electronegative than N.
• The Cl has a larger electron cloud (down one period) so there's a poorer match in orbital size/energy, so H-bonds are not common with Cl (but are technically possible - there are some examples in catalysis).

Hope this helps.

 

[idkkdi]

What you've described sounds like a hydrogen bond to me...an H-bond is essentially a special type of dipole-dipole bond.

For a hydrogen bond, you need:

1. A hydrogen bond donor: the component/molecule which supplies the hydrogen atom. The donor must have a sufficiently large charge separation, usually by being bonded to nitrogen, oxygen, or fluorine.
2. A hydrogen bond acceptor: the component/molecule with a lone pair (e.g. ketones, alcohols, amines, ethers). The accepting atom must have a high electron density (and a negative formal charge), typically nitrogen, oxygen, or fluorine.

Extended Discussion (non-syllabus):

• Hydrogen bond donors are distinct from typical dipole-dipole bonds because is significant orbital overlap so an H-bond is partially covalent (this is also what makes H-bonds directional).
• It comes down to matching orbital sizes/energies when you have N/O/F and an H-N/O/F, which enables this interaction.
• When people say H-bonding requires N/O/F because they are highly electronegative, they often ignore that Cl is more electronegative than N.
• The Cl has a larger electron cloud (down one period) so there's a poorer match in orbital size/energy, so H-bonds are not common with Cl (but are technically possible - there are some examples in catalysis).

View attachment 33264

Hope this helps.

wait so why is the second not a hydrogen bond

 

[Pedro123]

What you've described sounds like a hydrogen bond to me...an H-bond is essentially a special type of dipole-dipole bond.

For a hydrogen bond, you need:

1. A hydrogen bond donor: the component/molecule which supplies the hydrogen atom. The donor must have a sufficiently large charge separation, usually by being bonded to nitrogen, oxygen, or fluorine.
2. A hydrogen bond acceptor: the component/molecule with a lone pair (e.g. ketones, alcohols, amines, ethers). The accepting atom must have a high electron density (and a negative formal charge), typically nitrogen, oxygen, or fluorine.

Extended Discussion (non-syllabus):

• Hydrogen bond donors are distinct from typical dipole-dipole bonds because is significant orbital overlap so an H-bond is partially covalent (this is also what makes H-bonds directional).
• It comes down to matching orbital sizes/energies when you have N/O/F and an H-N/O/F, which enables this interaction.
• When people say H-bonding requires N/O/F because they are highly electronegative, they often ignore that Cl is more electronegative than N.
• The Cl has a larger electron cloud (down one period) so there's a poorer match in orbital size/energy, so H-bonds are not common with Cl (but are technically possible - there are some examples in catalysis).

View attachment 33264

Hope this helps.

A lot, thank you very much

 

[someth1ng]

wait so why is the second not a hydrogen bond

The hydrogen atom must be bonded to something highly electronegative (N/O/F) - this is what makes the bond highly polarised and able to form stronger intermolecular bonds.

All hydrogen bonds (at least, in Year 12 to maybe third-year university chemistry?) will follow this structure:

X and Y can be the same or different atoms.

 

[YourLocalDumbAss]

Apologies for questions, probably been answered before, just having a bit of a pre-HSC panic.
1. How come the intermolecular bonds formed with a carbonyl group on a molecule (i.e. carboxylic acid, or the non-carbonyl oxygen in the ester group) is defined as forming a dipole-dipole bond, but the bonds formed with the oxygen on the hydroxyl group are classified as hydrogen bonds, when both the carbonyl and the hydroxyl oxygen form them with a hydrogen? (This also applies for the amine group).

2. What is the order of bond strengths/boiling points for organic molecules or similar molar mass? I am under the impression it is:
- Alkanes, Alkenes, Alkynes
- Ketone
- Aldehyde
- Ester
- Alcohol
- Amine
- Carboxylic Acid
- Amide
But some assorted research has come up different? (Where amide and amine are higher than carboxylic acid and alcohol despite the lower strength H bonds due to the increased number of sites for H-Bonds to form)

Thanks

Nothing related to the question, but you still got Chemistry last. So stay calm, don’t panic, the more panic you have the less productive you are. Good luck